Science notes: Lightning in art and stick-insect survival

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A brown-eared bulbul eats a stick insect, R. irregulariterdentatus. New research suggests that tough eggs carried by bugs that mimic plants may be spread by hungry birds to new locations where they hatch.
(Hakuren Kato via The New York Times) - Bulletin

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A brown-eared bulbul eats a stick insect, R. irregulariterdentatus. New research suggests that tough eggs carried by bugs that mimic plants may be spread by hungry birds to new locations where they hatch.
(Hakuren Kato via The New York Times)7527737

Hungarian researchers have found that artists tend to paint lightning with fewer branches than the bursts of electricity actually have, according to a study published recently in Proceedings of the Royal Society A.

Their research points to how cultural legacies can distort our perceptions of natural phenomena, even those we encounter with our own eyes. Using a computer program, Gábor Horváth, head of the environmental optics laboratory at Eötvös Loránd University in Budapest, and his colleagues examined 100 paintings and 400 photographs of lightning. They found the pictures and paintings differed mainly in the number of root-like offshoots, which occur when charged particles try to carve the path of least resistance through air.

While painted lightning strikes had 11 arms at most, photographs showed lightning splitting into as many as 51 fingers. Actual numbers could be even higher, the authors noted, because some tendrils may be too dim for cameras to register.

In a follow-up experiment, the researchers asked 10 people to rapidly evaluate 1,800 photos each. They found that participants could accurately gauge up to 11 lightning branches. As the number of branches increased, people strongly underestimated the number of branches, with an exponentially growing gap between actual and perceived figures.

The finding is consistent with the ways humans are known to assess numbers, the authors noted. Below five, we’re able to subitize, or rapidly judge numbers of items without counting. Between six and 10, we count. Above 10, we estimate, with decreasing accuracy. This could explain why artists rarely portray lightning with more than 11 strands, Horváth said.

Simplified, zigzag images of lightning are also culturally ingrained (think of the lightning emoji or the common symbol for electricity). The imagery originated with ancient Greek and Roman depictions of Jupiter’s and Zeus’s thunderbolts, Horváth said.

Aphids are a familiar sight in the garden, sucking the juices out of your rose bushes. Luckily, so are ladybugs, which prey on aphids and keep them in check.

But the relationship between predator and prey is more complex than you might think. Aphids may be important to the survival of some ladybug species we have come to know and love by warding off another predator that has been moving in and feasting on them.

The arrival about 30 years ago in the United States of the multicolored Asian lady beetle, or Harmonia axyridis, which gleefully devours other ladybugs’ larvae, led to a drop in numbers of the seven-spotted lady beetle. Although the seven-spotted beetle is also an invasive species, it has been around longer than the Asian lady beetle, and exists alongside native ladybug species, which also take a beating.

However, some aphids contain a substance that’s much more toxic to this aggressive invader than to the other ladybugs. As a result, researchers show in a paper in the Proceedings of the Royal Society B, these aphids may provide refuge to the other ladybug species by killing off their common enemy.

The aphids in the study, which are themselves invasive, are all from the same species and all look exactly the same. But some are toxic to the Asian lady beetle and others are not. Although researchers still don’t know what the toxic substance is, whether aphids have it or not seems to depend on what plants they’ve been eating, as well as their parentage, says Paul Lenhart, an entomology researcher at the University of Kentucky.

In a field Lenhart’s team put both toxic and nontoxic aphids on plants, and also added Asian lady beetle larvae to some to see what would occur over the course of 10 days. In the final reckoning, nontoxic aphids fared very poorly when the Asian lady beetles were around, as did other ladybugs. But on plants with toxic aphids, there were not only more aphids, but other ladybug species were present in greater numbers.

This suggests that there may be ways for prey to protect predators that are less damaging than the alternative. That may help explain why some native ladybug species have held on despite having many invasive species to compete with.

Becoming bird food helps stick insects live on

It’s obvious why a stick insect’s wardrobe is the way it is. Look like a stick, avoid getting eaten.

But scientists in Japan noticed that despite their camouflage, stick insects became bird food quite frequently. And they also wondered: why do their eggs look like seeds?

In a paper published recently in the journal Ecology, the team of researchers suggest that these mostly flightless insects could sometimes benefit when they are eaten, using birds as carriers to disperse their eggs miles away, just like seeds. This passive dispersal mechanism could be why stick insects are found in places far from their original homes.

“It’s commonly assumed that when insects are eaten by birds, they and their unborn young have no chance of survival,” said Kenji Suetsugu, the leader of the study, a biologist who studies parasitic plants at Kobe University. But their results potentially overturn this dogma, he added.

Because plants can’t move around on their own, one way they disperse their seeds is by creating seed-containing fruits that animals eat. Thus, as animals travel, relieving themselves along the way, the plants travel too — through their seeds. But many birds also eat insects. So the researchers reasoned, that just like the fruits, the insects could be a means for dispersal, as long as their eggs can pass through the birds unharmed.

One thing that makes stick insect eggs different from most other insects is that they resemble seeds. And they’re coated in a chemical layer of calcium oxalate, the stuff humans find in kidney stones. Some of these eggs, carried inside females in certain stick insect species, also don’t need to be fertilized to hatch into viable offspring.

In 2015, Suetsugu and his team mixed dozens of these eggs into bird food and fed it to brown-eared bulbuls, birds that eat stick insects in Japan. A small percentage of the eggs from three species of stick insects made it through intact. But two years later, none had hatched.

However, they repeated the experiment in 2017, with 70 eggs from a single species. Twenty percent made it through, and 14 of those hatched, proving that it was possible for birds that consumed stick insects to drop their eggs like seeds to new locations.